JPH0321673A - Aqueous coating composition - Google Patents

Abstract

PURPOSE:To obtain the title composition having excellent dispersion stability and curing properties, capable of forming a coating film having excellent water resistance and film performance, containing a film-forming resin such as water- soluble resin or a compound for crosslinking agent solubilized in water. CONSTITUTION:The aimed composition containing (A) a water-soluble or water- dispersible film-forming resin (e.g. polyester containing carboxyl group, etc., neutralized with a basic substance and made water soluble) and (B) a compound for crosslinking agent made water soluble or water dispersible. The component B is preferably a substance prepared by co-condensing a water-insoluble alkyl etherified melamine resin with a compound, which contains a functional group to be reacted with the resin and has water solubility, under heating.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to new and useful aqueous coating compositions.

More specifically, it relates to a water-based coating composition that includes a water-based base resin component and a water-based crosslinking agent as essential components, and has particularly excellent curability, water resistance, and dispersion stability. .

[Conventional technology]

In recent years, from the perspective of environmental protection, there has been a demand to reduce the amount of organic solvents released into the atmosphere during the painting process.
This is being studied and considered as one of the countermeasures.

However, the water-soluble melamine resin that is commonly used for this type of water-based paint has a slow crosslinking reaction, and as a result, the water resistance of the cured film is poor, making it difficult to obtain sufficient paint film performance. For example, it requires vigorous baking at high temperatures, or requires the use of a curing catalyst, which has an adverse effect on other physical properties of the coating film other than water resistance.

Therefore, the use of water-insoluble alkyl etherified melamine resins, which have relatively good curing properties, in water-based paints is being considered, and one such attempt is to develop poly(meth)acrylic acid-based Although there is a method of water-dispersing such water-insoluble alkyl etherified melamine resin in the presence of a water-soluble resin, such as a resin, there is a drawback that the dispersion stability is insufficient. You can't miss it.

[Problem to be solved by the invention]

However, the present inventors have begun research on so-called aqueous coating compositions in which both the base resin and the crosslinking agent have been made water-based. We focused on improving the dispersion stability of the water-dispersed alkyl etherified melanin resin, and in addition, on obtaining an aqueous coating composition with excellent curability and water resistance of the coating film. We have repeatedly considered this as a goal.

Therefore, the problem to be solved by the present invention is to solve all of the various unresolved problems in the prior art as described above, and at the same time, to provide a solution that can be easily water-solubilized or water-dispersed and has stable dispersion. The purpose of the present invention is to provide an extremely useful compound for crosslinking agents that has excellent properties, and therefore has excellent dispersion stability and curability, as well as coating film performance such as water resistance. It is an object of the present invention to provide an excellent and highly useful aqueous coating composition.

[Means to solve the problem]

Therefore, the present inventors have conducted intensive studies to solve these various problems, and as a result, we have developed a method for using reactive polar groups (such as reactive polar groups such as hydroxyl groups, carboxyl groups, or amino groups).
A compound that has a functional group) and also has the ability to dissolve in water and a water-insoluble alkyl etherified melamine resin are heated and co-condensed, and then water is added to easily disperse the compound in water. We have discovered a compound for crosslinking agent that can be used as a crosslinking agent, and further proceeded to create a compound consisting of the compound for crosslinking agent obtained in this way and a water-soluble or water-dispersible film-form resin, which has not only good dispersion stability but also excellent dispersion stability. By discovering that the coating film has excellent curability and coating film performance such as water resistance, the present invention has been perfected. That is, the present invention requires, as essential precepts, a water-soluble or water-degradable film-form strong resin (A) and a water-soluble or water-dispersed crosslinking agent compound (A).
B), and more specifically, the above-mentioned film-type precept resin (A) is used as a base resin, and on the other hand, a non-water-soluble Alkyl etherified melane resin (b-1) and the resin (
A specific crosslinking agent compound obtained by co-condensing b-1) with a compound (b-2) having a reactive functional group and having water solubility under heating.
The present invention aims to provide an aqueous coating composition containing B) as a crosslinking agent.

Here, only typical examples of the above-mentioned water-soluble or water-dispersible film-forming resin (A) include polyesters, alkyds, etc. having acid groups such as carboxyl groups. It is made by neutralizing acrylic-modified polyester or acrylic-modified alkyd with a known and commonly used basic substance to make it water-soluble, or it is made by adjusting the degree of neutralization appropriately to make it water-dispersed. In addition, various nonionic surfactants such as polyoxyethylene nonylphenyl ether; or various anionic surfactants such as polyoxyethylene alkyl allyl ether sulfate; or 5 to about 150, and a number average molecular weight of 1. In the presence of a dispersion stabilizer such as various water-soluble resins such as acrylic resins having polyether side chains of 000 to 4.000,
For example, an acrylic monomer and various other copolymerizable monomers, if necessary, divinylbenzene, allyl methacrylate or ethylene glycol di(meth)
It is an aqueous dispersion with an average particle size of about 0.05 to 1 micron, which is obtained by polymerizing various crosslinkable monomers such as acrylate, and even hexamethoxymethylol. These include water-soluble melamine, such as melamine.

On the other hand... Examples of the water-soluble or water-dispersed crosslinking agent compound (B) include the water-insoluble alkyl etherified melagon resin (b-1) and the resin (b-1).
1) and a compound (b-2) that has a reactive functional group and is also soluble in water are co-condensed under heating to become water-soluble or water-dispersible. Something like this is particularly representative.

Here, the term "water-insoluble" in the present invention is
100n of 5g of the above alkyl etherified melamine resin
j! It is understood that this refers to water tolerance of 4 or less, which is expressed as the water dilution ratio at which the sample is collected in a beaker, mixed and diluted with deionized water, and the No. 1 type becomes unreadable through the beaker. sea bream.

To exemplify only particularly representative water-insoluble alkyl etherified melamine resins (b-1) according to this definition, examples of water-insoluble alkyl etherified melamine resins such as n-butyl etherified melamine or isobutyl etherified melamine These include methylolmelamine resins etherified with lower alcohols of C, ~C4, which have no solubility, and various water-insoluble alkyl etherified melamine resins (b
The functional group reactive with 1) has, for example, a hydroxyl group, an ξ-no group, or a carboxyl group, and
Examples of the compound (b-2) that also has solubility in water include compounds or resins having both a hydroxyl group or an amino group and a polyoxyethylene moiety; These include compounds or resins that have both an acid group and an acid group such as a carboxyl group.

The co-condensation reaction between the resin (b-1) listed above and the compound (b-2) is usually carried out using a ketone solvent such as methyl ethyl ketone or methyl isobutyl ketone, or methanol, ethanol, isobrobyl alcohol or n-butanol. It is carried out using an organic solvent such as a lower alcohol such as C or below, but water can also be used in combination if necessary.

At that time, the co-condensation reaction product obtained using the above-mentioned acid group-containing compound or resin as the compound (b-2) may be a known and commonly used compound such as ammonia, triethylamine or dimethylethanolamine. After being neutralized with a basic substance, on the other hand, the cocondensation reaction product obtained using a compound or resin having a polyoxyethylene moiety as mentioned above is treated as it is with water or, if necessary, A so-called aqueous medium consisting of water and an organic solvent such as a ketone or lower alcohol is added, and then the organic solvent is removed from the system under reduced pressure to achieve the desired water solubilization or water dispersion. A crosslinking agent compound (B) is provided. In preparing the cross-linking agent compound (B), each of the compounds has a water-insoluble alkyl etherified melamine resin (b-1) and a reactive functional group, and is soluble in water. Compounds that also have properties (
b=2) is used in a solid content ratio of about 10 to 100 parts by weight of the latter compound (b-2) to 1.00 parts by weight of the former resin (b-1). It is appropriate to fall within the following range.

If the amount of compound (b-2) used is less than about 10 parts by weight, the hydrophobic resin (
It becomes difficult to water-solubilize or water-disperse b-1),
Even if dispersion is achieved, two-layer separation may occur over time, or coarse particles may form.
As a result, this is undesirable because it results in a decrease in storage stability.On the other hand, if it is used in an excessively large amount exceeding about 100 parts by weight, the curability of the compound (b-2 ), for example, 4,0
When using one having a molecular weight of less than 0.00, it is not preferable because unreacted components will increase, which will have an adverse effect on various properties of the coating film.

For this reason, the number average molecular weight of this compound (b-1) is usually 4.000 to 100. 000, preferably 6,000 to ioo,ooo.

The blending ratio of the water-soluble or water-dispersible film-form resin (A) and the water-solubilized or water-dispersed crosslinking agent compound (B) obtained as described above is as follows: In terms of weight ratio, usually about 20 to 100 parts by weight of the latter compound (B) to 100 parts by weight of the former resin (A).
Appropriately, it is within a range of about parts by weight, and preferably
~ parts by weight is appropriate.

If the amount of compound (B) is less than about 20 parts by weight, curing properties tend to be insufficient;
If it is used in an excessive amount exceeding about 100 parts by weight, the viscosity of the paint will inevitably increase, resulting in poor painting workability or adversely affecting the water resistance and toughness of the cured paint film. Therefore, neither of these is preferable.

The aqueous coating composition of the present invention thus obtained can be used as a clear paint as it is, or it can be uniformly mixed with metallic pigments and/or colored pigments according to ordinary paint manufacturing techniques (painting method), respectively. It can also be a metallic or enamel paint.

In addition, the aqueous coating composition of the present invention may optionally contain a thixotropic agent, an anti-sagging agent, an anti-color separation agent, an anti-cissing agent, a surface tension regulator, an antioxidant, a light stabilizer, an ultraviolet ray Various additives such as absorbents and anti-settling agents may also be added as appropriate.
It can be blended.

The paint prepared using the aqueous coating composition of the present invention thus obtained can be used as it is, or in the form diluted with water or an aqueous solvent consisting of water and an organic solvent.
A coating that is applied by a conventional coating method such as spraying, dipping, or brushing, and then baked to provide a coating film with excellent hardening properties and various coating properties such as water resistance. It is.

Therefore, the aqueous coating composition of the present invention can be used for automobiles,
It is particularly useful for various metals such as motorcycles, electrical products, and cans.

〔Effect of the invention〕

The aqueous coating composition of the present invention first has excellent dispersion stability, secondly has excellent curability, and furthermore, can form a coating film with excellent coating performance including water resistance. Therefore, it provides an extremely useful coating film with well-balanced coating properties. [Example] Next, the present invention will be explained in more detail with reference to Reference Examples, Examples, and Comparative Examples. In the following, all parts and percentages are based on weight unless otherwise specified.

Reference Example 1 [Example of Preparation of Water-soluble Film-Type Resin (A)] 500 parts of isobrobyl alcohol and methyl ethyl ketone were added to a 4-liter colben equipped with a stirrer, a temperature control device, a condenser, a pressure reduction device, and a nitrogen introduction pipe. 500
The temperature was raised to 80℃, and then 100℃ of styrene was added.
parts, 390 parts of methyl methacrylate, 300 parts of n-butyl acrylate, 130 parts of 2-hydroxyethyl methacrylate, 80 parts of methacrylic acid and tert.
- Add a mixture of 20 parts of butyl peroctoate dropwise over 4 hours, maintain the same temperature for 8 hours to continue the polymerization reaction, and then add 80 parts of dimethylethanolamine and deionized water. plus 100 copies of 6
While maintaining the temperature at 0 to 80°C, isobrobyl alcohol and methyl ethyl ketone were distilled out of the system under reduced pressure, resulting in a mixture of water/isopropyl alcohol/
A solution of the desired vinyl resin was obtained with a solvent composition of methyl ethyl ketone = 89/6/5 (weight ratio) and a number average molecular weight of 18,000. ).

Reference Example 2 [Preparation example of water-dispersible film-form resin (A)] In a reaction vessel similar to Reference Example 1, 500 parts of methanol,
500 parts of methyl ethyl ketone and formula CH. CH. =C-C-0→CHZCHzO→-ii- CH
3 - (■) 400 of a compound with the structure shown by 11 0 (however, the average molecular weight of the polyoxyethylene part is about 4.000)
1 part, stirred, heated to 80°C, and
A mixture consisting of 300 parts of styrene, 270 parts of methyl methacrylate, 300 parts of n-butyl acrylate, 130 parts of 2-hydroxyethyl methacrylate and 20 parts of azobisisobutyronitrile was added dropwise over 4 hours, After the dropwise addition was completed, the same temperature was maintained for 8 hours to continue the polymerization reaction, then water was gradually added, thoroughly stirred, and methanol and methyl ethyl ketone were distilled out of the system under reduced pressure. 41.4%, and 2
Brookfield viscosity at 5°C is 22. OOOc
ps. A desired aqueous dispersion of vinyl resin was obtained. Hereinafter, this will be abbreviated as water-dispersible resin (A-2).

Reference Example 3 [Preparation example of water-dispersed compound (B) for crosslinking agent] Into the same reaction vessel as in Reference Example 1, 500 parts of methanol and 500 parts of methyl ethyl ketone were charged, and the temperature was raised to 80 ° C. Here, 100 parts of styrene, 390 parts of methyl methacrylate, 3 parts of n-butyl acrylate
00 parts, 130 parts of 2-hydroxyethyl methacrylate
A mixture of 80 parts of methacrylic acid and 20 parts of tert-butyl peroctoate was added dropwise over 4 hours, and after the dropwise addition was completed, the same temperature was maintained for 8 hours to continue the polymerization reaction. The desired aqueous dispersion of vinyl resin was obtained, with a Gardner viscosity of Y-Z" at 25° C. and a number average molecular weight of 17,000. Next, this aqueous dispersion was obtained. was used as a dispersion stabilizer, and 40 parts of "Super Becca Namen L-117-70BJ"
114.29 parts of butyl etherified methylol melamine (manufactured by Dainippon Ink & Chemicals Co., Ltd.) were charged into a 1 liter colben equipped with a stirrer, a temperature control device, a decanter and a nitrogen inlet tube, and heated to 80°C. When the reaction was carried out for 2 hours with stirring, the viscosity changed from Z to Z.
At this point, a mixed solvent consisting of 8 parts of dimethylethanolamine, 66 parts of deionized water, and 26 parts of isopropyl alcohol was added dropwise over 15 minutes, and then the mixture was poured into a decanter. When isobrobyl alcohol and methyl ethyl ketone were removed, the nonvolatile content was 50% and the Gardner viscosity at 25°C was Z. The desired aqueous dispersion of vinyl resin was obtained. Hereinafter, this will be used as a crosslinking agent compound (B-1
). Reference Example 4 (same as above) In a 2 liter glass reaction vessel equipped with a stirrer, temperature controller, decanter and nitrogen inlet tube, 69 parts of trimethylolpropane, 297 parts of neopentyl glycol, 91 parts of hydrogenated bisphenol A, 201 parts of isophthalic acid, 186 parts of tetrahydrophthalic acid, 155 parts of trimellitic anhydride, and 10 parts of xylene were charged, and the temperature was raised with stirring, and the reaction temperature was gradually increased from 180°C to 210°C.
When the reaction was continued for 5 hours while raising the temperature to ℃ and maintaining it within this range and removing the filtrate from the system, the acid value was 55, the hydroxyl value was 100, and A polyester resin having a number average molecular weight of 15,000 was obtained.

Next, 20 parts of this polyester resin and 114.29 parts of "Supervecamine L-117-70B J" were charged into a 1 liter colben equipped with a stirrer, a temperature control device, a decanter, and a nitrogen inlet tube, and a mixture of salanimethyl ethyl ketone was added. Add 50 parts of isobrobyl alcohol and 50 parts of isobrobyl alcohol, dissolve them uniformly, raise the temperature to 80°C while stirring, maintain the same temperature for 2 hours to continue the reaction, and add 50 parts of
The temperature was lowered to ℃, and a mixed solvent consisting of 1.5 parts of dimethyl ethanol agon, 66.7 parts of deionized water, and 31.8 parts of isopropyl alcohol was added dropwise over 15 minutes. After removing methyl ethyl ketone and isopropyl alcohol from the system, an aqueous dispersion of the desired modified melamine resin was obtained with a nonvolatile content of 49.7% and a Gardner viscosity of 2.0 or more at 25°C. Hereinafter, this will be referred to as a crosslinking agent compound (B-2).
It is abbreviated as

The thus obtained water-soluble or water-dispersible film-form resin (A) and the water-solubilized or water-dispersed crosslinking compound (B) are essential precepts, and if necessary, appropriate The aqueous coated composition of the present invention, which also contains various additives as listed above, can be diluted with water or an aqueous solvent consisting of water and an alcoholic solvent and/or a ketone solvent. Spray paint, for example, 140
Baking for 20 minutes at °C can give a clear coating, or on the other hand, such aqueous coating compositions can be used as metallic base coats by adding aluminum paste, repelling agents or flow modifiers, etc. Similarly, it was diluted with water or an aqueous solvent consisting of water and an alcohol-based solvent and/or a ketone-based solvent, and then spray-painted and pre-dried at 40-100°C for 1-5 minutes. Afterwards, a solvent-based or water-based clear coat is applied, and then, for example, 1
It is also possible to give a metal-like paint film by baking at 40 to 160°C for about 20 minutes. Examples 1 to 3 and Comparative Examples 1 to 3 Metallic base paints were prepared with the composition ratios shown in Table 1, and coated with an electrodeposited intermediate coating board [product of Nippon Root Service Co., Ltd.] by a conventional method. ], and then apply ``Acrydic GJ-110J [acrylic polyol manufactured by Dainippon Ink and Chemicals Co., Ltd.; TJi [min = 5
0%] / “Super Vesokamine L-127-75BJ
(Butylated melanin manufactured by the same company; non-volatile content = 75%
) = 7/3 (solid content weight ratio) solvent-based clear paint (solvent 1 "Solbefuso 100", "Solbesso 150")
J, a mixed solvent of xylene and n-butanol ("Solvesso" is a registered trademark of Exxon Chemical Co., Ltd.) was applied to obtain a two-coat finish.

Next, each coating film was baked at 160° C. for 20 minutes.

Thereafter, the performance of the thus obtained cured coating film was evaluated, and the results shown in the table were obtained.

Relationship between written amendment case and labeling case Patent applicant: 3-35-58 Sakashita, Itabashi-ku, Tokyo (288) Representative: Shigekuni Yomura, Dainippon Ink Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. Water-soluble or water-dispersible film-forming resin (A
) and a water-solubilized or water-dispersed crosslinking compound (B). 2. The above water-solubilized or water-dispersed crosslinking agent compound (B) reacts with the water-insoluble alkyl etherified melamine resin (b-1) and the resin (b-1). The aqueous coating composition according to claim 1, which is obtained by co-condensing the compound (b-2) with a water-soluble functional group and water solubility under heating. .